Putting the iPhone in DFU mode, a step that’s necessary in jailbreaking, is reported to be disabled with the Apple Mac OS X 10.5.6 software update. So if you’ve already got a jailbroken iPhone or iPod touch, you might want to look into using other machines for continued hacking, in the meantime.

If you still haven’t managed to get your iPhone jailbroken, then you’re going to have a hard time doing so now, if you’ve already updated to the latest version of Mac OS X using Apple’s provided software update. Various reportsconfirm that the software update does indeed directly disable DFU mode with iPhone and iPods in iTunes.

As to why this is happening, USB kexts are to blame. Noted iPhone developer Steven Troughton-Smith says it only happens when devices are plugged in directly to a Mac’s USB port, during which it is not recognized during DFU mode. However, DFU mode is available with a quick workaround: plugging your iPhone or iPod into a USB hub first, before plugging the hub into the USB port of the Mac.

This move by Apple isn’t entirely surprising. It seems that the company is still against jailbreaking, which is the first step towards unlocking a phone for use with any network across the world. But all would-be jailbreakers only have to realize that this problem would probably go away soon, and it’s up to their discretion whether they should update and settle for the workaround or just wait to update when the problem is confirmed to be cleared.